A plasma processing, such as, a dry etching, representatively, is a process for conducting micro-processing on a semiconductor, so as to obtain a desired configuration thereof, through etching of parts other than mask portions on a surface of a sample to be processed, while exposing the sample to be processed to a gas, being brought into plasma through electromagnetic waves, which is introduced into a vacuum container having a vacuum exhaust means. Upon uniformity of processing within a sample surface to be processed, the followings have ill influences; i.e., distribution of plasma, distribution of temperature within the sample surface to be processed, and/or distribution of composition of a gas supplied and a flow rate thereof, etc. In particular, in such plasma processing apparatus of parallel plate type, as is disclosed in the following Japanese Patent Laid-Open No. 2011-9249, since the gas is supplied from a shower plate, on which a large number of fine gas through holes are formed, to be disposed opposing to the sample to be processed, and the distance between the sample to be processed and the shower plate is relatively short, the distribution of supply of the gas, which is supplied from the shower plate gives an ill influence upon a processing rate and/or an etching profile, etc. The plasma processing apparatus of the parallel plate type, practically utilizing this characteristic, has an advantage of enabling to control the distribution of the processing rate and/or the shape within the sample surface to be processed, and thereby obtaining a uniformity desired.
However, in the plasma processing apparatus of parallel plate type, a strong radio-frequency electric field, for forming plasma, lies in the vicinity of the shower plate, and because of this electric field, there are sometimes produced cases where electric discharge is generated within gas through holes, which are formed on the shower plate. The electric discharge within the gas through hole produces generation of a particle and/or contamination, from a conductive material, etc., which is disposed on a rear surface of the shower plate. This also gives an ill influence on the etching profile at the position of the sample surface to be processed, corresponding to the position where the electric discharge is generated within the gas through hole, i.e., to be a cause of reason of defects. Further, generation of the electric discharge within the gas through hole increases an amount of ablation of the shower plate through hole, then brings about a problem of shortening a cycle of exchanging the shower plate and increasing a manufacturing cost, etc.
For dealing with such the problem as was mentioned above, normally, it can be considered to make a diameter of the gas through hole to be formed or treated on the shower plate, as small as possible. For example, applying the gas through hole of 0.1 mm to 0.5 mm, so as to heighten a probability of annihilation of an electron on a side wall of the through hole, it is possible to reduce a risk of the electric discharge within the gas through hole. However, only with such small-sizing of the diameter of the gas through hole, substantially, it is impossible to prevent the electric discharge from being generated within the gas through hole, but rather this rather results into a restriction of condition for electric discharge (i.e., restrictions of electric power for electric discharge and/or the flow rate of a supply gas, etc.) Also, the small-sizing of the gas through hole brings up a processing cost of the shower plate to be expensive, i.e., a cause of reason of increasing the cost. Moreover, normally, for the purpose of discharging the gas, uniformly, there is a necessity of bringing the positions of the gas through holes, which are treated on a conductor portion to be located on a rear surface of the shower plate, to be coincide with the positions of the gas through holes to be treated on the shower plate; however, if the diameter of the gas through hole is small, it is difficult to bring them to be coincide with, from a viewpoint of accuracy, and then there are brought about cases where a uniformity of gas supply on a surface goes down and/or a reproducibility of gas supply cannot be obtained.
In the Japanese Patent Laid-Open No. 2011-9249 is also disclosed a plasma processing apparatus, for suppressing an abnormal electric discharge to be produced within the gas through holes of the shower plate, wherein an upper electrode is made of a shower plate, on which first gas through holes are treated with, a conductor plate, on which second gas through hole are treated with, to be disposed on a rear surface of the conductor plate, an insulator plate, on which third gas through holes are treated with, to be located at a central portion of the conductor plate, and an antenna substrate portion having a temperature controlling function and a gas distribution portion, to be disposed in the rear surface of the conductor plate, and a first very small gap is defined in a radial direction on a boundary surface between the shower plate and the insulator plate, a second very small gaps is defined in the radial direction on a boundary surface between the insulator plate and the conductor plate, and centers of the first gas through holes are shifted from those of the third gas through holes, in a peripheral direction or the radial direction.
However, with this apparatus, it is possible to suppress the abnormal electric discharge at the central portion of the conductor plate; however, no consideration is paid on suppression of the abnormal electric discharge in portions other than the central portion. Also, the first gas through holes and the third gas through holes mentioned are shifted from, but no consideration is paid, fully, on shortage of conductance of a gas flow due to shifting between those first gas through holes and the third gas through holes.
As a result of the above, with such conventional structure of the shower plate, there can be considered cases where a processing capacity or performance with applying the plasma cannot be taken out, due to restriction of the etching condition, lowering of the uniformity, and further lowering of the reproducibility thereof.